Accommodation (eye)

Human Lens Scheimpflug layers

Accommodation (eye) is the process by which the eye changes optical power to maintain a clear image (focus) on an object as its distance varies.

Mechanism of Accommodation

In humans, accommodation involves three movements: changing the curvature of the crystalline lens, changing the size of the pupil, and converging the eyes. The ciliary muscle, a ring of smooth muscle in the eye's middle layer (vascular layer), controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humour into Schlemm's canal. It changes the shape of the lens within the eye, not the size of the pupil which is carried out by the sphincter pupillae muscle and dilator pupillae.

Accommodation Reflex

The accommodation reflex (or accommodation-convergence reflex) is a reflex action of the eye, in response to focusing on a near object, then looking at a distant object (and vice versa), comprising coordinated changes in vergence, crystal lens shape and pupil size (accommodation).

Disorders of Accommodation

Disorders of accommodation can occur and these include presbyopia, accommodative insufficiency, accommodative excess, accommodative infacility and ill-sustained accommodation. These disorders can often be corrected with glasses or contact lenses, or managed with vision therapy.

See Also

• Presbyopia
• Myopia
• Hypermetropia
• Astigmatism (eye)

References

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